Lusitania (Portuguese: Lusitânia) was an ancient Roman province including approximately all of modern Portugal south of the Douro river and part of modern Spain (the present autonomous community of Extremadura and a small part of the province of Salamanca).

It was named after the Lusitani or Lusitanian people (an Indo-European people).

It was initially part of the Roman Republic province of Hispania Ulterior, before becoming a province of its own in the Roman Empire.

Romans first came to the territory around the mid 2nd century BC.

A war with Lusitanian tribes followed, from 155 to 139 BC. In 27 BC, the province was created.